Bluetooth: hci_qca: fix potential GPF

In qca_power_shutdown() qcadev local variable is
initialized by hu->serdev.dev private data, but
hu->serdev can be NULL and there is a check for it.

Since, qcadev is not used before

	if (!hu->serdev)
		return;

we can move its initialization after this "if" to
prevent GPF.

Fixes: 5559904c

 ("Bluetooth: hci_qca: Add QCA Rome power off support to the qca_power_shutdown()")
Cc: stable@vger.kernel.org # v5.6+
Cc: Rocky Liao <rjliao@codeaurora.org>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>